Flat intramedullary nail

ABSTRACT

The intramedullary nail for treating a fracture of a long bone according to the present invention has the shape of a helically twisted blade with a flattened cross section extending partially or totally along the longitudinal axis of the nail. The nail is provided with a hole at its distal end for receiving a bone fixation means to be inserted transversely through the hole and at least one cortex of the long bone. The nail is made long and thin with the smallest dimension of the cross section being much smaller than the largest dimension, so that it is flexible along the longitudinal axis of the nail.

FIELD OF THE INVENTION

This invention relates to an intramedullary nail having the shape of ahelically twisted blade and at least one hole at one of its free ends.The intramedullary nail is especially suited for the humerus and forother long bones where the insertion plane is different from the lockingplane. It is also suited for long bones of young children where thegrowth plate should not be disturbed.

BACKGROUND OF THE INVENTION

In recent years, the intramedullary nail has gradually gained importanceand is becoming a standard method of internal fixation. Since thedevelopment of this method by Küntscher, the intramedullary nail hasbroadened its range of indications (e.g. locking nail, Gamma nail,reconstruction nail).

The basic concept behind nailing has remained the same, namely theintroduction of a tube or full cylinder into the medullary cavity of atubular bone. Initially, nailing was used for the femur, but now, itsapplication has been extended to include all large tubular bones. Untilnow, the cross-sections of intramedullary nails have remained more orless the same. Even the cloverleaf cross-section developed by Küntschersome 50 years ago is still being used today, even though it has beenproven that this shape brings no special advantages. Additionally,changing the cross-section from the circular or almost circularcross-section was never considered necessary before, since the medullarycavity of the various tubular bones was usually opened using a rotatingor circular cutting device.

Today, more attention is being paid to the rate of fracture healing, andit is believed that healing occurs faster if less damage is done to thebone during placement of an implant in the body. By choosing anappropriate cross-sectional shape for an intramedullary nail whichcorresponds to the anatomy of the medullary canal, it is possible toeliminate unnecessary removal of bone and tissue from the medullarycanal, thus promoting healing by minimizing damage to the medullarycanal and its vascularization.

The choice of nail cross-section is particularly relevant for thehumerus bone, in which the medullary canal is not round along its entirelength but is in fact flat and thin in the distal part. For this bone, anail with the typical circular or almost circular cross-section wouldnot be appropriate. A nail with a flattened cross-section would be moresuited for the distal humerus.

SUMMARY OF THE INVENTION

The opening of the medullary canal for insertion of the nail can alsocause unnecessary damage to the bone, as well as to the surrounding softtissue and joint. Intramedullary nails are typically stiff and aretraditionally inserted through an insertion site which is in line withthe longitudinal axis of the bone.

For the case of the humerus bone, antegrade insertion (i.e. insertionfrom the shoulder end of the humerus) typically goes directly throughthe rotator cuff. This can cause irreparable damage to the joint capsuleand instability of the shoulder joint, and can result in post-operativepain and/or loss of range of motion of the limb.

For the case of growing young bones, insertion sites in line with thelongitudinal axis of the bone tend to interfere with the growth plate,which can affect the normal development and growth of the bone. An“ideal” insertion site avoids both the joint for long bones, as well asthe growth plate in young patients. For the humerus, an ideal antegradeinsertion site is located slightly distal to the greater trochanter onthe lateral aspect, thus completely avoiding the joint capsule androtator cuff at the shoulder. This ideal insertion site can not be usedwith traditionally stiff nails, and could only be used with nails whichwould be flexible along their length.

The invention as claimed aims at solving the above described problems byproviding an intramedullary nail whose flexibility is achieved byrelying on the natural mechanical properties (i.e, modulus ofelasticity) of the nail material.

The nail is made long and thin with the smallest dimension of thecross-section being much smaller than the largest dimension, so that itis flexible along the longitudinal axis of the nail.

If such a thin, flat nail is inserted into the humerus using the ideal,antegrade, lateral insertion site described above, the distal part ofthe flat nail will be oriented 90° to the flat distal humerus. In orderto correct this orientation problem of the flat distal nail in the flatdistal humerus, the nail is twisted 90°, or any multiple of 90°, alongits length. This does not significantly affect the local bendingproperties of the nail (i.e. short length along the axis), since bendingcan still occur at any one longitudinal section. Retrograde insertion(i.e. insertion from the elbow end of the humerus) of this flat nailinto the humerus is not affected by this twist, since the proximalhumerus is relatively large, has a round cross-section, and allows thedistal part of the nail to be oriented in any way inside the proximalhumerus. Therefore, this flat, twisted nail is suitable for bothantegrade and retrograde insertion into the humerus.

For long, thin, flat nails, the 90° twist of the nail has an additionaladvantage: to bring added bending stability to the longitudinal device.A flat longitudinal device, after implantation, may bend in themedullary canal under a bending load. With an added longitudinal twist,however, the device is more stable longitudinally and is, thus, lesslikely to bend in the canal during normal limb activity.

For thin, flat nails, the 90° twist of the nail has yet anotheradvantage, related to locking for both an antegradely- orretrogradely-inserted nail. For a locking hole to be designed through anail, the cross-sectional dimension orthogonal to the hole axis must begreater than the diameter of the locking hole. Depending of course onthe diameter of the locking bolt, this may not be possible for the thin,flat nail design if the locking hole goes through the largest dimensionof the cross-section, i.e. through the thickest wall. From an anatomicalpoint of view, the presence of nerves and other important tissues canalso limit the possibility of locking directions. In the proximalhumerus, the brachial plexus nerve group located antero-medially shouldbe avoided during locking. Thus, for a retrograde nail, the safestlocking in the proximal humerus is in the lateral-medial direction. Incontrast, for an antegrade nail, locking in the flat distal humerus ismost commonly done in the posterior-anterior direction, i.e. through thethinnest wall of the humerus.

Therefore, to satisfy anatomical and mechanical requirements forlocking, the proximal and distal locking holes and screws should beoriented 90° (or a multiple of 90°) to each other.

For a thin, flat cross-section such as for the invention described here,this can only be achieved with a nail which is twisted 90°, or multipleof 90°, along its length.

For the purpose of closing a fracture gap, a wire or cable loop, asdescribed in U.S. Pat. No. 5,034,012, can be added to the nail accordingto the invention.

The wire/cable can be looped around the entire length of the nail,preferably inset in slots, grooves or other shape of opening on thenarrow sides of the flat cross-section of the nail. The closed end ofthe wire or cable (i.e. the looped part) at the distal tip of the nailis protected from being damaged or deformed during insertion by a metalU-shaped part surrounding it, which is part of the nail. The two ends ofthe wire/cable at the open end of the loop are fixed inside a nut, whichis inside the proximal part of the nail. To reduce a fracture gap usingthis wire/cable loop design in the flat, thin nail design, the lockingbolt is first placed at the far end of the nail through the locking holeand the loose wire/cable loop. The inner nut is then rotatedcounter-clockwise with a screwdriver, causing the nut to move upwardsand the wire/cable to be pulled upwards. As this is done, the wire/cableloop around the locking bolt at the distal part of the nail becomessmaller, tightly encloses the locking bolt, and finally pulls thelocking bolt towards the proximal part of the nail. This applies acompressive force between the proximal and distal bone fragments, thusreducing the fracture gap.

To summarize the important points, the first main advantage of theflattened, twisted nail is that it is flexible in bending, which allowsit be inserted from more anatomical insertion sites not necessarily inline with the longitudinal axis of the bone. As explained above, this isparticularly important for the proximal humerus to avoid the shoulderjoint capsule and rotator cuff, as well as for pediatric long boneswhere the growth plate should be avoided. The twist allows not onlylocking advantages but also makes the nail generally more stable inbending after insertion into the medullary canal.

Another main advantage of this nail is that its flat, thincross-section, when used in the humerus, corresponds to the shape of themedullary cavity of the distal humerus. It therefore requires no extrabone or tissue to be removed before nail insertion. As well, the small,anatomical cross-section does not significantly disturb thevascularization in the medullary canal, which is important for fracturehealing.

The various features of novelty which characterize the invention arepointed out with particularity in the claims annexed to and forming partof this disclosure. For the better understanding of the invention, itsoperating advantages and specific objects attained by its use, referenceshould be had to the accompanying drawings, examples and descriptivematter in which are illustrated and described preferred embodiments ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawing:

FIG. 1 is a perspective view of the intramedullary nail according to theinvention, shown inserted antegradely into humerus and locked distallywith a locking screw;

FIG. 2 is a partial representation of the lower part of the nailaccording to FIG. 1 seen from an 90° angle;

FIG. 3 is a cross-section of the nail according to FIG. 1 at the lineIII—III;

FIG. 4 is a modified cross-section of the nail according to theinvention;

FIG. 5 is a further modified cross-section of the nail according to theinvention;

FIG. 6 is a further modified cross-section of the nail according to theinvention;

FIG. 7 is a further modified cross-section of the nail according to theinvention;

FIG. 8 is a partial longitudinal cross-section through the upper part ofthe nail according to FIG. 1; and

FIG. 9 is partial enlarged representation of the lower part of the nailaccording to FIG. 1 with the cable in the lowest position.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 to 3 show an intramedullary nail consisting of a helicallytwisted blade 1 having a hole 2 at its distal end 4. The nail may have afurther hole 2 towards its proximal end 3. The blade 1 is twisted about90° around its longitudinal axis 5 in a continuous way.

The length L of the blade 1 is in the range of 150 to 300 mm and theratio T/W between the thickness T and width W of said blade 1—asrepresented in FIG. 3—is in the range of 0,035 to 0,286, preferably inthe range of 0,1 to 0,2.

The flat intramedullary nail is used conventionally as shown in FIGS. 1and 2 for treating a fracture of a long bone 6 by inserting itlongitudinally into the medulla 7 of a long bone 6, and securing theintramedullary nail to the long bone 6 in its longitudinal position bybone fixation means 8, preferably in the form of screws, to be insertedtransversally through the hole 2 and at least one cortex 9 of the longbone 6.

The head 10 at the proximal end 3 of the intramedullary nail is shown inmore detail in FIG. 8 in order to describe how to assemble theintramedullary nail of FIG. 1. One end of a preferably metallic cable(or wire) 11 is inserted through the head 10 and then threaded throughgroove 12 on the right side of the nail until it exits into hole 2 asshown in more detail in FIG. 9. The one end of cable 11 pushed into hole2 is then threaded back up through groove 13 on the left side of thenail until it exits in the head 10.

At this point both ends of cable 11 are protruding out of head 10 at theproximal end of the nail, and towards the distal end 4 of the nail,cable 11 forms a loop at locking hole 2.

Both ends of cable 11 are then inserted into the cavity of an innerhollow tube 15. To secure cable 11 in said inner tube 15 the cable 11 isfirst adjusted for length and then inner tube 15 is deformed at position16 in at least one plane. Threaded tube 17 is slid over inner tube 15and the assembly 15,17 is threaded into the interior threads 19 ofhollow head 10 by means of tool geometry 18, resulting in twisting ofcable 11, until threaded tube 17 is at its lowest position inside head10. If the cable length was properly adjusted before being fixed insideinner tube 15, the loop 14 of cable 11 will now be at its lowestposition inside slot 2 at the distal end 4 of the nail as shown in FIG.9. The nail is now assembled and ready for implantation in theintramedullary cavity of a long bone.

An insertion handle (not shown) is fixed on head 10 of the nail usingthe interior threads 19. The nail is implanted in the usual fashion inthe humerus or other long bone in the body. The insertion handle isremoved. The nail is now ready to be locked distally.

Free-hand distal locking is performed through slot 2 in the usualfashion with a locking bolt or screw 8. The elongated hole or slot 2 iseasier to locate for, compared to traditional holes, resulting in easierfree-hand locking. After distal locking, a tool (not shown), e.g. aslotted screwdriver is used at tool geometry 18 through open end 20 ofhead 10 to unthread (or raise) threaded tube 17 until the loop 14 ofcable 11 in slot 2 contacts and applies pressure to the locking bolt orscrew 8 as shown in FIG. 1.

The advantage of the nail according FIG. 1 over nails according to theprior art, e.g. 7 mm diameter nails, is the easier free-handdistal-locking due to the elongated hole 2, while still offering theadvantage of secure bolt/screw fixation, provided by the loop 14 ofcable 11 around the bolt/screw.

The configuration of blade 1 of the nail can be varied in several ways.

FIG. 3 shows the embodiment with lateral grooves 12 and 13 guiding cable11.

FIG. 4 shows an alternative embodiment in which the grooves 12 and 13 ofFIG. 3 are replace by closed tunnels in which cable 11 is lodged.

FIG. 5 shows a further embodiment which is interesting from a point ofview of manufacturing. It consist of a simple metal sheet forming blade1 the lateral side of which have been curved in order to form lateraltunnels taking up cable 11.

FIGS. 6 and 7 are just other variations of the embodiment according toFIG. 5 and which are easy to manufacture.

The advantage of the nail according FIG. 1 over prior art small-diameterflexible nails, e.g. 2 to 4 mm, is that it offers improved stability dueto the interlocking possibilities. Interlocking is usually not possiblefor small-diameter nails, due to the material limitation. In otherwords, there is not enough material to insert a locking screw throughit.

While the foregoing description and drawings represent the preferredembodiments of the present invention, it will be obvious for thoseskilled in the art that various changes and modifications may be madetherein without departing from the true spirit and scope of the presentinvention.

What is claimed is:
 1. An intramedullary nail having a longitudinal axisfor fixation of a fractured bone having a medullary canal, theintramedullary nail comprising a helically twisted blade ofpredetermined thickness, length and width and having a distal end with adistal hole for receiving a first bone fixation element for securing thedistal end to the bone and a proximal end with a proximal hole forreceiving a second bone fixation element for securing the proximal endto the bone, wherein at least a portion of the blade has a flatten crosssection extending along the longitudinal axis of the nail and throughthe medullary canal of the bone and wherein the proximal and distal endslie substantially within the medullary canal.
 2. The intramedullary nailof claim 1 wherein the ratio of blade thickness to blade width is about0.035 to 0.286.
 3. The intramedullary nail of claim 1 wherein the bladetwists from about 30° to 200° about a longitudinal axis of the blade. 4.The intramedullary nail of claim 3 wherein the blade twists continuouslyabout the longitudinal axis of the blade.
 5. The intramedullary nail ofclaim 1 further comprising an insertion element located at the proximalend of the blade for inserting and removing the intramedullary nail fromthe bone.
 6. The intramedullary nail of claim 5 wherein the insertionelement comprises an internally threaded portion on the proximal end ofthe blade for receiving a threaded insertion handle.
 7. Theintramedullary nail of claim 1 wherein the first and second bonefixation elements each comprise a cortical screw.
 8. The tramedullarynail of claim 1 wherein the proximal and distal holes are perpendicularwith respect to the longitudinal axis of the intramedullary nail.
 9. Theintramedullary nail of claim 1 wherein the distal hole is elongatedalong a longitudinal axis of the nail.
 10. The intramedullary nail ofclaim 1 wherein the blade length is from about 150 to 300 mm.
 11. Theintramedullary nail of claim 1 wherein the blade cross section iselliptical.
 12. The intramedullary nail of claim 1 wherein a largestdimension of the blade cross section is from about 6 to 20 mm.
 13. Theintramedullary nail of claim 1 wherein the blade width is no less thanabout 0.3 to 5 mm.
 14. The intramedullary nail of claim 1 wherein theintramedullary nail is made of sheet metal or tubing having a wallthickness from about 0.2 to 3.5 mm.
 15. The intramedullary nail of claim1 wherein the intramedullary nail is made of a polymeric sheet having awall thickness from about 0.5 to 5 mm.
 16. The intramedullary nail ofclaim 1 further comprising a pair of channels in the blade for receivinga cable or wire for closing a fracture gap in the fractured bone. 17.The intramedullary nail of claim 16 wherein each channel of the pair ofchannels is located on a side of the blade and has a substantiallyU-shaped cross section.
 18. The intramedullary nail of claim 16 whereineach channel of the pair of channels has a substantially circular crosssection with a diameter from about 0.8 to 3 mm.
 19. An intramedullarynail for fixation of a fractured bone comprising: a helically twistedblade of predetermined thickness, length and width and having a distalend with a distal hole for receiving a first bone fixation element forsecuring the distal end to the bone and a proximal end with a proximalhole for receiving a second bone fixation element for securing theproximal end to the bone; a pair of channels in the blade for receivinga cable or wire for closing a fracture gap in the fractured bone; and aU-shaped cover at the distal end of the blade operatively associatedwith each channel of the pair of channels to allow the wire or cable toloop around from one of the channels to the other channel, wherein atleast a portion of the blade has a flattened cross section.
 20. Anintramedullary nail for fixation of a fractured bone comprising: ahelically twisted blade of predetermined thickness, length and width andhaving a distal end with a distal hole for receiving a first bonefixation element for securing the distal end to the bone and a proximalend with a proximal hole for receiving a second bone fixation elementfor securing the proximal end to the bone; a pair of channels in theblade for receiving a cable or wire for closing a fracture gap in thefractured bone; and a inner tube for receiving ends of the wire or cableand an outer tube for receiving the inner tube and having a threadedouter surface, wherein the proximal end of the blade includes a chamberhaving threaded walls for receiving the outer tube and rotation of theouter tube into the chamber tightens the wire or cable to close thefracture gap and wherein at least a portion of the blade has a flattenedcross section.